I'd tend to agree with Roger: If you're renting to begin with (and getting paid, thats the important part - if not, your D50 will take pictures that are JUST FINE!) go with a full frame (D3s, D3, D700) and a 24-70 2.8. Again, if you're renting, and do not have an external flash, rent an SB-900 as well.
All that said, I've had my D300 since it came out, and wouldn't hesitate to use it!
Cheers,
Mark